A follow-up program of a large number of patients with aorto-coronary vein bypass operation has enabled us to obtain over 500 samples of vein grafts removed at autopsy or during a second revascularization procedure. The time interval between the first bypass operation and removal of the graft ranged from few hours to 10 years. We propose to study these grafts in detail using advanced immunohistochemical and electron microscope methods to learn about the processes which contribute to the development of atherosclerosis and closure of the vein grafts.